April 13, 2011 -- Brain shrinkage seen on MRI imaging may actually occur up to 10 years before Alzheimer's disease is diagnosed, finds a new study in Neurology.

"This measure is potentially an important imaging marker of early changes in the brain associated with Alzheimer's disease that could help predict who might develop the dementia associated with this disease and possibly even how long it would be before dementia develops," says study researcher Bradford Dickerson, MD, a neurologist at Harvard Medical School in Boston, in a news release. "These are preliminary results that are not ready to be applied outside of research studies right now, but we are optimistic that this marker will be useful in the future."

About 5.4 million people in the U.S. have Alzheimer's disease, a progressive brain disease that leads to a decline in memory and other cognitive abilities. It is the most common form of dementia, according to the Alzheimer's Association.

There is no single test that can diagnose Alzheimer's, but an early diagnosis could lead to more therapeutic opportunities.

Measuring Brain Shrinkage

Researchers used magnetic resonance imaging (MRI) brain scans to measure specific areas of the brain that are known to be involved in Alzheimer's in two groups of people with no memory issues or signs of Alzheimer's disease. In one group, 33 people were followed for about 11 years, during which eight of them went on to develop Alzheimer's disease. Another group of 32 people were followed for about seven years, and seven developed Alzheimer's disease, the study showed.

Those with smaller brain size in these key areas were about three times more likely to develop dementia over the following 10 years than those with higher measurements, the study showed.

Marc L. Gordon, MD, a neurologist and Alzheimer's disease researcher at The Feinstein Institute for Medical Research in Manhasset, N.Y., says that those who went on to develop to Alzheimer's dementia already had thinning of the cerebral cortex in areas of the brain involved in early Alzheimer's disease at the beginning of the study, compared with those who didn't develop Alzheimer's.

"Relatively small, but reproducible differences in cortical atrophy (brain shrinkage) may be identified in asymptomatic individuals nearly a decade before the onset of dementia, and this may be a useful early imaging biomarker for predicting risk of subsequent dementia," he says in a news release.